Serotonin levels, pain threshold, & fibromyalgia (FM) symptoms in the general population

OBJECTIVE: To investigate the association of serum serotonin
with fibromyalgia (FM), and to study the relationship of
serotonin to clinical variables associated with FM.

METHODS:
Serum samples (n = 292) were obtained on subjects without
pain, with regional pain, and with widespread pain during a
population survey. The tender point examination was made
according to American College of Rheumatology examination
criteria by an examiner blind to the subjects' complaints.

Serotonin was determined by high performance liquid
chromatography coupled to an electrochemical detector.

RESULTS: No associations between clinical variables and
serotonin levels were found in the group as a whole. Subjects
with FM had lower serotonin levels unadjusted (p = 0.019) and
adjusted for age and sex (p = 0.059) than those without FM.
Within the FM group, associations between serotonin and
tender point count (r = 0.563) and depression (r = 0.549)
were noted, but the direction of association was opposite to
previous reports and expectations.

CONCLUSION: Serum
serotonin levels are significantly lower in persons with FM
compared to those without FM, but the range of values is
wide. Difficult to explain correlations with reversed
directions are noted for tender point count, dolorimetry,
depression, and anxiety among those with FM. Serotonin is not
correlated with any clinical variables in the general
population, and separate pain groups cannot be distinguished.